The present invention relates to a storage medium and an apparatus and a method of recording and reproducing encoded data thereto and therefrom. Particularly, this invention relates to a writable storage medium, and an apparatus and a method of recording and reproducing signals, such as, audio, video and bitmap video signals to and from the storage medium.
With the development of recent information processing technology, digital audio and/or video signals are compressed for recording onto storage media. Optical discs have been considered as one of main storage media for random accessibility and portability.
Moving picture signals require advanced compression techniques for efficient usage of limited storage capacity of storage media due to their large amounts of data compared to audio signals.
Among such compression techniques, data compression processing using the inner frame correlation within one frame (unit of picture) and the correlation between frames that are close to each other on the time base are well known.
These data compression techniques require variable bit rate (VBR) compression encoding processing that results in substantial variation of data amount per frame of moving pictures according to complexity of frame pictures and the degree of correlation between frames.
On the other hand, audio signals are mostly compressed by constant bit rate (CBR) compression encoding processing that produces encoded data of constant bit rate per predetermined period of time due to relatively small amount of data of audio signals.
In addition to moving picture video signals and audio signals, bitmap video signals require compression encoding processing when stored on storage media.
Bitmap video signals are used for overlaying subtitles on moving pictures, for instance. Moving picture signals, audio signals and bitmap video signals are recorded on digital versatile discs (DVDs). Subtitles of bitmap video signals can be selectively displayed because they are encoded separately from moving pictures. Bitmap video signals are also used for overlaying graphics to modify moving pictures.
Storage media, such as DVDs, for storing those signals are formed with successive sectors thereon. Each sector is used for storing a small but constant amount of data. Encoded data are separately stored on the sectors. Access (read/write) to these media is usually performed for each sector. Encoded data of moving picture signals, audio signals and bitmap video signals are stored on different sectors for better accessibility.
These encoded data are recorded on a storage medium in the form of program bitstream that is defined by ISO/IEC13818-1 (MPEG standards) to meet the following requirements:
Encoded data of moving picture signals, audio signals and bitmap video signals are multiplexed for recording on sectors of a storage medium because these signals are in synchronism with each other. The rate of reading these signals from the storage medium is controlled in accordance with the bit rates of the moving picture signals that have been compressed by the VBR compression encoding processing.
Program bitstreams of encoded data are recorded on a storage medium so that packs (unit of data transfer) and sectors exactly meet each other. Each pack carries encoded data of signals, such as, moving picture signals, audio signals and bitmap video signals. Encoded data of these signals are multiplexed in unit of pack. Each pack also carries time data, such as, a system clock reference (SCR) , for controlling the rate of signal reading. The packs also include several data, such as, data for identifying the encoded data.
Recording encoded data with multiplexing in unit of pack as disclosed above is, however, disadvantageous in after-recording compared to usual audio/video recording, for example, by VHS (Registered Trademark) video tape recorders.
VHS offers after-recording for recording audio signals only to follow video signals already recorded on a magnetic tape.
In VHS systems, video signals are separated into luminance signals and crominance signals. The luminance signals are modulated by frequency modulation. On the other hand, the crominance signals are converted into frequencies lower than the frequency-modulated luminance signals. Audio signals are frequency-modulated into the frequencies between the converted crominance signals and the frequency-modulated luminance signals.
These signals are processed by frequency-division multiplex and recorded on a magnetic tape by rotary magnetic heads. The signals are recorded as analog signals on main tracks that are inclined in the longitudinal direction of the magnetic tape. In addition, the audio signals are recorded as analog signals by a fixed magnetic head on audio-recording tracks in the longitudinal direction of the magnetic tape. The audio-recording tracks offer after-recording of audio signals.
Compared to the after-recording in VHS systems, recording of encoded data with multiplexing in unit of pack as disclosed above is, disadvantageous in after-recording due to the following reasons.
Illustrated in FIG. 1 is that encoded data of video signals V1, V2 and V3 are only recorded as packs on a storage medium. SCRs are also recorded for transfer rate control that eliminates spare sectors (no signal recorded) between the sectors on which encoded video signals are recorded.
After-recording of audio signals to follow the video signals recorded as shown in FIG. 1 requires multiplexing of new packs into the packs of video signals. For such multiplexing, many packs of encoded data of video signals have to be moved onto other sectors for insertion of new packs of encoded data of audio signals.
Such pack movement during recording requires complicated control. In addition, high pack rate areas of moving picture signals, such as, the area IV shown in FIG. 1 will not accept insertion of packs of audio signals. These problems will also occur for after-recording of bitmap video signals.